The present invention relates to a method for manufacturing lithographic printing plates from presensitized plates for used in making lithographic printing plates (hereinafter referred to as "PS plates") and more particularly to a method for manufacturing lithographic printing plates by developing an imagewise exposed PS plate and then treating the plate with a finisher.
There has conventionally been known a method for manufacturing lithographic printing plates from PS plates which generally comprises developing the PS plate after imagewise exposing it to light and then treating the developed PS plate with a finisher such as a rinsing solution containing a surfactant or a protective gumming solution comprising a water-soluble resin, in order to save the amount of washing water used after development (see, for instance, Japanese Patent Un-examined Publication (hereunder referred to as "J. P. KOKAI") Nos. Sho 55-115045 (U.S. Pat. No. 4,291,117) and Sho 55-12921).
ln addition, a method in which a developed PS plate is washed with washing water which is repeatedly utilized, is also known (see J. P. KOKAI No. 55-25027). After such a cyclic water washing process, the PS plate processed is then generally treated with the foregoing finisher.
Finishers are preferably acidic or neutral ones from the viewpoint of neutralizing an alkaline developer remaining on a lithographic printing plate during the plate-making process. However, if a part of such an alkaline developer is carried over to a bath containing a finisher during the plate-making process, gel-like insoluble matters are liable to be formed. This makes the maintenance and washing of an automatic developing machine and so forth inconvenient and complicated, and causes the clogging of a spray pipe; and the insoluble matters are adhered to lithographic printing plates as contaminants. For this reason, it is difficult to use a finisher for a long time period without exchanging the same.
The inventors of this invention have examined thoroughly to elongate the life span of a rinsing solution and already found that the rinsing solution can be stabilized by performing rinsing in a plurality of rinsing baths to gradually decrease the concentration of a developer while gradually reducing pH of the rinsing baths so that the later bath has a lower pH (see J. P. KOKAI No. Sho 63-172270).
This method makes it possible to greatly increase the time of forming gel-like substances in the rinsing solutions and to stably perform processing for a long time period. However, in the later rinsing baths, such gel-like substances ar gradually formed as the pH value of the rinsing baths reaches around 7 or more.